The present invention relates to the field of deep drilling; in detail, it regards a device for consolidating soils by means of mechanical mixing and injection of consolidating fluids.
The consolidation of soils envisages the drilling of a hole using a drilling device. During the drilling step, or at the end thereof operations are carried out, designed to increase the characteristics of solidity of an area of soil corresponding substantially to the hole or to areas adjacent thereto.
It is known that the operations of consolidation can use the technologies described in detail hereinafter.
A first technology is the so-called “mechanical dry mixing”, which is frequently used for soils in which a fair amount of water is present; the use of this technique envisages insertion of cement in powder form in the soil, exploiting, for example, air compressed at pressures that typically do not exceed 30 bar and a mixing tool equipped with rotating blades fixed with respect to the battery of drilling rods.
A second technique is the so-called “low-pressure wet-mixing”, where the consolidation is provided via a jet of fluid made up of a mix of water and concrete (typically known as “grout”). Once again the jet of fluid is characterized by a low pressure (up to a maximum of approximately 40-50 bar) through a tool equipped with blades that are able to mix the soil with the above-mentioned fluid.
A third technique is finally the so-called “high-pressure mechanical wet-mixing”.
With this third technique, the treatment for consolidating soil is performed by means of an injection of a jet of high-pressure (typically approximately 100-400 bar) grout coming out of the barrel of a drilling and injection tool equipped with mixing blades (typically in a radial position).
In this way, a minimum diameter of the consolidated area is guaranteed by the presence of the mixing blades (and for this reason the term “mechanical minimum” is used) and a maximum diameter thereof is guaranteed by the pressure of the consolidation fluid. In detail, in fact, the consolidation fluid could also come to operate on areas of soil not reached by the extent of the mixing blades of the drilling and injection drilling tool.
With particular reference to the third and last technique described, the mixing of the soil can occur during the drilling (downwards) or else at the end of the drilling (upwards) or in both direction according to the type of soil to be treated.
For particular requirements of design (for example, in the case where earth removal operations are envisaged after the foundations of a building have laid or the necessary treatments of the soil have carried out) it may be required for mechanical mixing to be performed only in a portion of soil localized at a certain depth. In this case, in the sector, the term “idle traverse” is used, which describes the procedure through which the drilling and mixing tools, which are equipped with radially set extensible blades, pass from the plane of site to a height of treatment, remaining with the blades closed in such a way as to guarantee a minimum drilling diameter. Said solution enables drilling to be speeded up and rendered more economically advantageous.
There exist tools that are able to execute an initial drilling of contained dimensions and that, when a desired depth is reached, via opening-out of some mechanical components resembling cutters, referred to as “mixing blades”, carry out a drilling operation or simply mixing of the soil with an injected consolidating fluid, on a diameter much greater than that of the lower depth.
The mixing of the soil is conveniently carried out downwards in the case of easily worked soils; instead, in the presence of “difficult” soils, mixing is preferably carried out upwards, after prior execution, during the initial step of descent, of an operation of injection of even different fluids (a step technically referred to as “pre-cut”) in order to lighten the soil and prepare it for the subsequent mixing.
As regards the drilling, cutting and mixing devices, multiple documents are known in the prior art.
For instance, the document No. U.S. Pat. No. 7,195,080 teaches how to solve the problem inherent in the uniqueness of the drilling diameter that can be provided by cutting means (cutters) in the working configuration. The document No. U.S. Pat. No. 7,195,080 moreover teaches how to render the cutters more rigid through blocking means that reduce the vibrations thereof during operation.
In detail, the document No. U.S. Pat. No. 7,195,080, shows a tool for widening a bore hole during a step of descent in depth, which can exploit, for the movement of radial opening of its cutting means (cutters):                hydraulic energy, through insertion of a linear actuator (jack) connected to a position indicator (indexer) that enables modulation of the opening of the aforesaid blades so as to obtain variability in the drilling diameter;        other forms of energy, such as for example electrical energy, via provision of an electric motor and/or other simple mechanical devices.        
In detail, the hydraulic energy is supplied either via dedicated fluid or using the same fluid used for excavation (bentonite). This fluid actuates a jack that displaces axially a body, which opens the cutters out by levering on a plurality of fulcra. Following upon entrance of the pressurized fluid, blocking means are pushed against the cutters. Once the desired depth has been reached, at the end of the drilling operation the delivery of the dedicated fluid or the drilling fluid (bentonite) is interrupted so that the blocking means are free to move, with consequent release of the cutters, which can close again automatically until they are brought into the initial position.
The technique described by the preceding document does, however, present some disadvantages. In fact, with this technique it is not possible to act with the drilling fluid (bentonite) during the drilling step, keeping the cutters closed. Furthermore, the document does not teach the possibility of injecting consolidating fluid different from the drilling fluid (bentonite). Finally, according to the known art represented by the document No. U.S. Pat. No. 7,195,080, the drilling head must necessarily present a passage or mechanical means purposely dedicated to the system of movement of the blades in the case where these are moved by mechanical and electrical means. In detail moreover, the movement of the blades via electrical means can be decidedly inconvenient and delicate, given the working environment.
Not of least importance, the U.S. document does not teach how to make a head that is effective and will enable consolidation both working downwards and working upwards.